Farmers in eastern China are resorting to vuvuzelas, gongs, firecrackers and bombs to ward off wild boar that are threatening their crops.

Local officials in Zhejiang say the animal population has increased fivefold in the past 10 years because villagers - their main predator - are moving into the cities and gun licences have been restricted as part of the security arrangements for the Shanghai Expo.

The hungry animals are said to be moving from their mountain forest homes to forage in farmland and the residential suburbs of Hangzhou.

Local people have responded with traps, electric fences and a cacophony of noise. According to the Xinhua news agency, the racket has been made by traditional instruments, karaoke machines and South African-style vuvuzela.

"The growing wild boar population is now a disaster to our village and neighboring ones. We knock on gongs, explode firecrackers and even use bombs, but there are just so many," Wang Aihua of Fangwu village told Xinhua.

Local media have been filled with warnings of the impact on crops and other species. Corn yields in the worst affected area are expected to fall by one-third because so many plants have been trampled upon.

Neighbouring Jiangxi province reported a similar problem last month and issued 7,200 hunting licenses to cull the boar population.

In Zhejiang, this has been difficult because the province borders Shanghai, which is currently hosting the Expo, a high-profile world fair that has prompted a tightening of shotgun controls.